It is the goal of the proposed research to evaluate the effects of hypertension on the microcirculation, and to delineate the participation of the precapillary resistance vessels in the development of hypertension. These problems are being studied in the cremaster muscle and the mesentery of the spontaneously hypertensive rat and will be expanded to DOCA-salt and 1-Kidney Goldblatt hypertensive models using the gracilis muscle preparation. The research project will determine if there are reduced numbers of small arterioles in the hypertensive animals, if there is an increased wall/lumen ratio, and if the changes found are the cause or effect of hypertension. Comparisons among the different models of hypertension will separate hereditary and model-specific microvascular adaptations from more universal alterations. Measurements of red cell velocity will be made in arterioles, capillaries, and venules. Arteriolar blood flow will be calculated from the velocity data and the lumen diameter, measured from a video monitor. Density of microvessels per unit area of tissue will also be determined by quantitative stereological techniques. The data will be analyzed by grouping the vessles according to branching order, and comparing the measurements in hypertensive animals to those found in normotensive controls.